In recent years, the photonics industry is developing vigorously, making great progress in various areas including image display, signal transmission, and lightings.
In the field of lightings, the light source required in most of cases is a white light source. A tungsten lamp used in the past is eliminated gradually due to high power consumption and poor luminous efficiency. Nowadays, there are many kinds of ways to generate the white light source, in which the way that a blue laser diode is used as a pumping source, and yellow phosphor is plated onto the outside of the lampshade, may be more commonly used. When a blue light emitted from the blue laser diode passes through the lampshade, a portion of blue light may be absorbed by the yellow phosphor to generate a yellow light complementary to the blue light. Then, a white light is generated by means of color mixture.
The problem of a lower luminous efficiency occurs in the presently commercially available white light source, however, owing to the restriction of a smaller light-emitting area of the blue laser diode. Moreover, such a white light source obtained by the mixture of two colors is composed of only two monochromatic light waves, in such a way that the spectrum distribution is monotonous, resulting in a poorer color rendering index (CRI) with more restricted fields of application.
A general white LED lighting lamp is not satisfactory in the place, where a higher CRI of lighting source is required, such as a printing industry, textile factories, hotels, shops, hospitals, schools, precision machining factories, office buildings, and houses, for example. The requirement for higher CRI of light source is even needed more in the field applications including color inspection, clinical diagnosis, and art gallery lighting.